Re: [boost] Re: [Boost Python Library] Mixing types wrapped in different modules

From: Ullrich Koethe (koethe_at_[hidden])
Date: 2000-12-07 12:59:53

I strongly agree that this is a very important extension. Here is an
example that might be a little easier to explain:

Given two modules:

- uimodule.so: contains wrapped C++ user interface widgets
  including, say, "Window"
- logicmodule.so: contains application logic and a new widget
"ResultsWindow" 
  derived from "Window"

Now the problem is: how can we use "ResultsWindow" like any window
defined in the UI module, *without* merging the two modules into one?

I think it can already be done with BPL. (At least, the following worked
in my tests.)

1. wrap the UI classes into uimodule.cpp as usual.

2. in uimodule.cpp: define functions to retrieve the class object for
   any class needed in another module:

    boost::python::detail::extension_class<Window> * get_window_class()
    {
      return 
        dynamic_cast<boost::python::detail::extension_class<Window> *>
        (boost::python::detail::class_registry<Window>::class_object());
    }

   Declare these functions in a header "uicommon.hpp"

3. Wrap the application logic and "ResultWindow" into logicmodule.cpp 
   as usual:

    boost::python::class_builder<ResultWindow> 
              reswindow_class(logicmodule, "ResultWindow");

4. in logicmodule.cpp: 
   - Include  "uicommon.hpp"
   - declare the wrapped "Window" as base of the wrapped 
     "ResultWindow"

    reswindow_class.get_extension_class()->
                         declare_base(get_window_class());
     
5. *Dynamically* link logicmodule.so against uimodule.so

     g++ -shared -o logicmodule.so logicmodule.o uimodule.so \
         -lboostpython

6. Then in Python

   >>> import ui
   >>> import logic
   >>> result_window = logic.ResultWindow()
   >>> ui.show(result_window)     

Function show() from module ui can be applied to an object from module
logic!

[Note: to make this work, line 33 in module_builder.cpp must be
commented out:
     //    assert(name_holder.get() == 0);
]

David, is there anything inherently wrong with this? It certainly works
in a simple test setting.

Regards
Ulli

-- 
 ________________________________________________________________
|                                                                |
| Ullrich Koethe  Universität Hamburg / University of Hamburg    |
|                 FB Informatik / Dept. of Computer Science      |
|                 AB Kognitive Systeme / Cognitive Systems Group |
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